Method of making electrolyte paste



Patented Feb. 9, 1943 METHOD OF MAKING ELECTROLYTE PASTE Richard Miiller and Barry Lee, Radebeul, near Dresden, Germany; vested in the Alien Property Custodian No Drawing. Application June 8, 1940, Serial No.

339,526. In Germany June 7, 1939 2 Claims.

This invention concerns an electrolyte paste, as it finds use in so-called dry cells or dry batteries.

In making and applying such a paste, more particularly in ammoniumor magnesium-chloride cells, the following procedure has been generally followed in the past:

The electrolyte, e. g. ammonium-, zinc-, magnesium-chloride etc., is dissolved in water in a stirring vat. After the chloride has been dissolved, a thickening or gelatinizing agent is added. Ordinarily wheat flour serves as such an agent. The mixture is then stirred and filled into the cells see Ziegenberg, Trockenelemente and Batterien, published in Berlin-Schdneberg, 1934, pages 39 and 226).

The said procedure has been found to involve certain disadvantages, more particularly when stiffening or gelatinizing agents are used which are difficult to wet, such as lignine, peat, etc. When the agent is added after the electrolyte solution has been prepared, minute bubbles of air adhere to each particle of the powder ofthe agent, and these bubbles cannot be removed from the electrolyte paste. In terms of colloidal chemistry the mixture represents a more or less perfect foam.

Since the paste must be prepared to be of comparatively high viscosity, it is not possible for the minute bubbles of air to escape from the electrolyte paste, even if they become detached later on from the particles of the gelatinizing agents, to which they adhered in the beginning. When the electrolyte paste is cooked up, those bubbles are expanded by the heat, the paste is driven up in the zinc cup, and the cell foams and overflows.

But it was further determined by various tests for electrical efliciency performed after different periods of storage of a cell, that cells made in accordance with established procedure exhibit more or less premature corrosion depending upon the gelatinizing agent used. Each and every little bubble of air, which has been retained in the paste of the electrolyte and comes into contact with the zinc cup, is the cause for an uncontrolled local attack upon the zinc cylinder, and at each of these points the cylinder is prematurely destroyed.

It is an object of this invention to prevent such phenomena of corrosion to the greatest possible extent. Thus the preparation and conditioning of the gelatinizing agent, e. g. the drying process thereof, may be controlled in such manner, that air adhering to the product is displaced the agent was removed, so that the powder would not absorb air afterwards.

Although. this process of air re'placemen was very efl'ective in reducing COI'IOSlOD. in the cell, it did not fulfill another object of this invention, i. e. it did notovercome the obnoxious foaming of the electrolyte during cooking, when the finished cell becomes warm etc. During and after the prepaartion of an electrolyte paste according to such a process there will be more or less of a nitrogen loam, which entails the same objectionable foaming and overflowing which accompanies all processes of the prior art, although in this case there is no corrosion of the zinc.

Further experimenthas led to the surprising result, that both of the objects stated above may be obtained in an extremely simple manner. If a thorough wetting of the gelatinizing agent by the electrolyte is provided for right from the start, the undesirable foam is not permitted to form in the first instance. In a preferred embodiment of the invention the gelatinizing agent is therefore not introduced into the electrolyte solution, but the electrolyte solution is, for instance, added gradually, step by step, to the dry gelatinizing agent while the mixture is being homogenized, be that by stirring with a pestle or, upon a larger scale, by grinding or powder mills or rollers, or other homogenizing apparatus. Such procedure yields an electrolyte paste, which is free of foam, and which does therefore not exhibit the unwanted foaming or overflowing, nor does it cause any phenomena of corrosion of the zinc cup.

Example 1 45 grams of finely ground and sifted peat and 22 grams of wheat flour are placed into a grinding bowl. 25 com. of an electrolyte are added, which contains 250 grams of ammonium chloride, grams of zinc chloride and 2.5 grams of mercuric chloride per liter of water, and the mass is vigorously stirred with a pestle. Slowly more of the electrolyte solution is added, while the mass is being reduced by vigorous working to a stiff, homogeneous paste of even consistency, until eventually a total of 400 com. of electrolyte solution have been introduced. The mass does not foam, stifiens most readily in cooking, does not Example 2 180 com. of an electrolyte which contains 20 grams of zinc chloride, 20 grams of manganous chloride, and 3 grams of mercuric chloride per liter of a saturated magnesium chloride solution of 35 B., are added in the manner described in Example 1 step by step to a mixture of 45 grams of a finely powdered lignine residue of saccharification of wood and 22 grams of wheat flour. The resultant; mass does not foam, stitfens readily, does not overflow, nor does it exhibit any phenomena of corrosion.

When such procedure is followed in the preparation of an electrolyte paste, the thickening or gelatinizing agent is completely wetted, so that all the disadvantages mentioned first above are overcome and avoided, and the various objects of this invention are fully attained.

The gelatinizing agents of the foregoing examples are preferable under nitrogen, or nitrogen is introduced during dissolution as explained first above.

The foregoing description and various changes and ments may be made within pended claims.

We claim:

1. Method for preparing an electrolyte paste for a dry cell which is free of air, comprising displacing the contents of air of the gelatinizing agent by placing it under an atmosphere of an inert gas, mixing the agent with an electrolyte and passing an inert, water-insoluble gas through the mixture.

2. Method for is merely illustrative alternative arrangethe scope of the appreparing an electrolyte paste which is free of air, comprising displacing the contents of air of the gelatinizing agent by placing it under an atmosphere of an inert, waterinsoluble gas, and then gradually stirring the electrolyte into said agent.

RICHARD Milunn. HARRY LEE. 

